In chloroplast anatomy, what are grana (singular: granum) and what is their primary role in photosynthesis?

• A. Pigment-containing protein complexes in the cytosol that synthesize glucose during the dark reactions
• B. Stacks of thylakoid membranes that house photosystems and are the main site of the light-dependent reactions
• C. Fluid-filled region (stroma) where the Calvin cycle enzymes are located and carbon fixation occurs
• D. Openings in the leaf epidermis (stomata) that regulate gas exchange and water loss

Answer: (B)

Verified step by step guidance

1. Identify the structure referred to as grana (singular: granum) within the chloroplast. Grana are stacks of thylakoid membranes.
2. Understand that thylakoid membranes contain pigment-protein complexes, including photosystems, which are essential for capturing light energy.
3. Recognize that the primary role of grana is to serve as the main site of the light-dependent reactions of photosynthesis, where light energy is converted into chemical energy (ATP and NADPH).
4. Distinguish grana from other chloroplast components such as the stroma, which is the fluid-filled region where the Calvin cycle (light-independent reactions) occurs.
5. Note that grana are not related to pigment-containing complexes in the cytosol or stomata, which are involved in different processes like glucose synthesis or gas exchange.